1. Field of Invention
This invention relates to a method, and system for inducing global cerebral hypothermia while maintaining normal core temperature for the prevention of secondary brain injury from stroke, trauma, or surgery.
2. Description of Prior Art
Patients suffering from stroke or head trauma, or have undergone invasive brain or vascular surgery are at risk from secondary brain injury. Secondary brain injury is a result of the innate healing response of the brain to the original insult caused by several not completely understood mechanisms. Regardless of the specific mechanisms involved, the end result is swelling of the brain caused by edema, which can lead to a critical or terminal rise in intra-cranial pressure.
It has long been known that hypothermia is neuroprotective. Hypothermia has a positive affect on all know mechanisms that lead to secondary brain injury. Hypothermia is routinely used during brain and other invasive surgeries to protect the brain from surgical interruptions in blood flow. Hypothermia has also been shown to be effective in controlling swelling of the brain in trauma and stroke patients.
The effectiveness of hypothermia is a function of depth and duration; the deeper the hypothermia, and/or the longer it is applied the more neuroprotective it is. However, hypothermia has historically been applied systemically, and the depth and duration of hypothermia is limited by the patient's ability to tolerate the therapy.
Systemic hypothermia has historically been accomplished by immersion of the patient's body in a cool bath. Today there are several commercial systemic hypothermia systems available. They consist of blankets or pads where cooled water is circulated through channels in the walls of the blanket or pad, and the patient's body is maintained in intimate contact. Medivan Corp. manufactures an example of a modern hypothermia system under the trade name Arctic Sun Cooling System.
Systemic hypothermia has been demonstrated to be effective in reducing secondary injury from stroke, trauma, and surgery however, there are several drawbacks to this approach: 1) It takes several hours to lower a patient's body to therapeutic temperatures. This delay in achieving therapeutic temperatures allows for the progression of irreversible secondary injury to the brain. 2) The practical therapeutic hypothermic temperature and duration is limited by the ability of the patient to tolerate, or survive the therapy. 3) The side effects of systemic hypothermia are frequent and can be life threatening, especially in frail patients. Side effects include shivering, cardiac arrhythmia and arrest, pneumonia, infections, and coagulation disorders. 4) The target of hypothermia therapy is the brain; therefore inducing hypothermia systemically places the patient at undue risk. 5) During the “critical phase” (rewarming period) of hypothermia treatment, there is no effective way to manage a sudden and critical increase in intra-cranial pressure, since re-cooling the body to reverse the increase in intra-cranial pressure takes several hours. 6) Systemic hypothermia poses significant clinical and logistical patient management issues.
There are several examples in the art where catheters are constructed with a cooling means, which is placed into the carotid artery to cool the blood entering the head. This offers an advantage over systemic hypothermia, since it provides a means to cool the head to lower temperatures than the rest of the body, but it still results in systemic hypothermia. Also, since the scientific evidence suggests that hypothermia must be maintained for extended periods of time, there is a great risk that clots will form on the catheters and migrate into the brain leading to episodes of stroke.
Barbut et al. (U.S. Pat. No. 6,217,552) suggests that cerebral hypothermia may be accomplished by placing a catheter in a lateral ventricle of the brain, and a second catheter into the subarachnoid space, and then pumping cooled fluid from the first catheter in the lateral ventricle to the second catheter in the subarachnoid space where the fluid flows from the lateral ventricle, through the third ventricle, and into the subarachnoid space via the cerebral aqueduct. This approach may be effective in inducing cerebral hypothermia in a normal healthy brain; brains that are suffering ischemia or trauma are often swollen. Swelling of the brain compresses the ventricles and cerebral aqueduct which prevents or limits fluid flow between the lateral ventricle, and the subarachnoid space. One significant problem with inducing cerebral hypothermia by cooling the cerebrospinal fluid in the ventricles is that it results in systemic hypothermia due to the fact that the brain is highly vascular, and that up to ⅓ of the body's heat is generated in the brain. Barut does not suggest a means of maintaining normal core temperature while inducing cerebral hypothermia by ventricle cooling.
Nowhere in the art is it suggested that directly cooling the walls of a ventricle of the brain may induce global cerebral hypothermia and therefore prevent secondary brain injury. Nowhere in the art is it suggested that cerebral hypothermia can be accomplished by removing the cerebrospinal fluid from a brain ventricle, then inflating a balloon within said ventricle, and then cooling the walls of said ventricle with said balloon. Nowhere in the art is a means taught for inducing cerebral hypothermia by ventricle cooling while maintaining normal core temperature.